Method for reducing the content of an unsaturated amine in a mixture containing an amine and a nitrile

ABSTRACT

A process is provided for reducing the content of a monounsaturated aliphatic amine (III) in a mixture (IV) containing an aminonitrile (I) or a diamine (II), or mixtures thereof, and the amine (III), wherein  
     a) the mixture (IV) is reacted with an anionic nucleophile (V),  
     which contains a nucleophilic atom selected from the group comprising oxygen, nitrogen and sulfur,  
     which is capable of taking up an H +  ion to form an acid with a pK a  ranging from 7 to 11, measured in water at 25° C., and  
     which has a relative nucleophilicity, measured in methyl perchlorate/methanol at 25° C.,  
     ranging from 3.4 to 4.7 when oxygen is the nucleophilic atom,  
     ranging from 4.5 to 5.8 when nitrogen is the nucleophilic atom, and  
     ranging from 5.5 to 6.8 when sulfur is the nucleophilic atom,  
     in an amount ranging from 0.01 to 10 mol per mole of amine (III) in the mixture (IV), to give a mixture (VI), and  
     b) the aminonitrile (I) or the diamine (II), or mixtures thereof, are distilled from the mixture (VI) at a temperature ranging from 50 to 170° C. and a pressure ranging from 0.5 to 100 kPa.

[0001] The present invention relates to a process for reducing thecontent of a monounsaturated aliphatic amine (III) in a mixture (IV)containing an aminonitrile (I) or a diamine (II), or mixtures thereof,and the amine (III), wherein

[0002] a) the mixture (IV) is reacted with an anionic nucleophile (V),

[0003] which contains a nucleophilic atom selected from the groupcomprising oxygen, nitrogen and sulfur,

[0004] which is capable of taking up an H⁺ ion to form an acid with apK_(a) ranging from 7 to 11, measured in water at 25° C., and

[0005] which has a relative nucleophilicity, measured in methylperchlorate/methanol at 25° C.,

[0006] ranging from 3.4 to 4.7 when oxygen is the nucleophilic atom,

[0007] ranging from 4.5 to 5.8 when nitrogen is the nucleophilic atom,and

[0008] ranging from 5.5 to 6.8 when sulfur is the nucleophilic atom,

[0009] in an amount ranging from 0.01 to 10 mol per mole of amine (III)in the mixture (IV), to give a mixture (VI), and

[0010] b) the aminonitrile (I) or the diamine (II), or mixtures thereof,are distilled from the mixture (VI) at a temperature ranging from 50 to170° C. and a pressure ranging from 0.5 to 100 kPa.

[0011] Mixtures containing an aminonitrile or a diamine, or mixturesthereof, and an unsaturated amine—an unsaturated amine being understoodin terms of the present invention as meaning a cyclic or linear compoundcontaining at least one carbon-nitrogen double bond or a compoundcapable of forming at least one carbon-nitrogen double bond, for exampleby an elimination reaction—are conventionally obtained in the partialhydrogenation of dinitriles to aminonitriles or a mixture ofaminonitriles and diamines, or in the complete hydrogenation ofdinitriles to diamines.

[0012] The partial hydrogenation of adipodinitrile (ADN) with thesimultaneous production of hexamethylenediamine (HMD) and6-aminocapronitrile (ACN), and the complete hydrogenation of ADN to HMD,in the presence of a catalyst based on a metal such as nickel, cobalt,iron, rhodium or ruthenium, is generally known e.g. from K. Weissermel,H. -J. Arpe, Industrielle Organische Chemie (Industrial OrganicChemistry), 3rd edition, VCH Verlagsgesellschaft mbH, Weinheim, 1988,page 266, U.S. Pat. No. 4,601,859, U.S. Pat. No. 2,762,835, U.S. Pat.No. 2,208,598, DE-A 848 654, DE-A 954 416, DE-A 42 35 466, U.S. Pat. No.3,696,153, DE-A 19500222, WO-A-92/21650 and DE-A-19548289.

[0013] The byproducts formed are, inter alia, azepine derivatives suchas N-(2-azepano)-1,6-diaminohexane, N-(2-azepano)-6-aminocapronitrileand, in particular, 2-aminoazepan and tetrahydroazepine (THA).

[0014] These azepine derivatives, which cause coloration and impair theproduct properties and are therefore unwanted impurities in theaminonitriles and diamines conventionally used for the manufacture ofsynthetic fibers or engineering plastics, can be separated from theaminonitriles, diamines or mixtures thereof only at considerableexpense.

[0015] EP-A-497333 describes the separation of aliphatic aminonitrilesor aliphatic diamines from mixtures containing an aliphatic aminonitrileor aliphatic diamine and a cyclic, monounsaturated aliphatic amine bythe addition of bases, the base being used in stoichiometric excessrelative to the cyclic, monounsaturated aliphatic amine. Basesrecommended for this separation are alkali metal hydroxides, alkalineearth metal hydroxides, tetraalkylanmonium hydroxide, alkali metalalkoxides and alkaline earth metal alkoxides.

[0016] The disadvantage of this process is a simultaneous polymerizationof valuable product which leads to an appreciable loss of valuableproduct and to unwanted deposits in the apparatuses and machines usedfor carrying out the process.

[0017] It is an object of the present invention to provide a process forreducing the content of a monounsaturated aliphatic amine in a mixturecontaining an aminonitrile or a diamine, or mixtures thereof, and amonounsaturated aliphatic amine, in a technically simple and economicmanner which avoids said disadvantages.

[0018] We have found that this object is achieved by the process definedat the outset.

[0019] Suitable aminonitriles (I) are compounds containing one or more,such as two, three or four, nitrile groups, preferably one nitrilegroup, especially compounds containing at least one nitrile group whichis located adjacent to an aliphatic carbon atom carrying one or two,preferably two, hydrogen atoms, or mixtures of such aminonitriles.

[0020] Suitable aminonitriles (I) are compounds containing one or more,such as two, three or four, amino groups, preferably one amino group,especially compounds containing at least one amino group which islocated adjacent to an aliphatic carbon atom carrying one or two,preferably two, hydrogen atoms, or mixtures of such aminonitriles.Particularly preferred aminonitriles are those containing a terminalamino group, i.e. an amino group located at the end of an alkyl chain.

[0021] The aminonitrile (I) is preferably based on an alkyl skeleton.

[0022] In a preferred embodiment, the aminonitrile (I) has from 4 to 12carbon atoms.

[0023] Suitable aminonitriles (I) are preferably selected from the groupcomprising 4-aminobutyronitrile, 5-aminovaleronitrile,2-methyl-5-aminovaleronitrile, 6-aminocapronitrile and12-aminododecanenitrile, especially 6-aminocapronitrile.

[0024] Such aminonitriles can be prepared in a manner known per se.

[0025] 6-Aminocapronitrile can be obtained by the partial catalytichydrogenation of ADN with a gas containing molecular hydrogen to givemixtures containing HMD and ACN.

[0026] Catalysts which can advantageously be used in this hydrogenationare those based on a metal selected from the group comprising ruthenium,rhodium, nickel, cobalt and, preferably, iron, it being possible for thecatalysts to contain other elements as promoters. In the case ofiron-based catalysts, suitable promoters are especially one or more,such as two, three, four or five, elements selected from the groupcomprising aluminum, silicon, zirconium, titanium and vanadium.

[0027] Such catalysts and the process conditions for said reaction aredescribed for example in WO-A-96/20166, DE-A-19636768 and DE-A-19646436.

[0028] Suitable diamines (II) are compounds containing two or more, suchas two, three or four, amino groups, preferably two amino groups,especially compounds containing at least two amino groups which arelocated adjacent to an aliphatic carbon atom carrying one or two,preferably two, hydrogen atoms, and particularly preferably diaminescontaining terminal amino groups, i.e. amino groups located at the endof an alkyl chain, or mixtures of such diamines.

[0029] The diamine (II) is preferably based on an alkyl skeleton.

[0030] In a preferred embodiment, the diamine (II) has from 4 to 12carbon atoms.

[0031] Suitable diamines (II) are preferably selected from the groupcomprising 1,4-diaminobutane, 1,5-diaminopentane,2-methyl-1,5-diaminopentane, 1,6-diaminohexane (HMD) and1,12-diaminododecane.

[0032] Such diamines can be prepared in manner known per se.

[0033] HMD can be obtained by the partial catalytic hydrogenation of ADNwith a gas containing molecular hydrogen to give mixtures containing HMDand ACN, or by the complete hydrogenation of ADN with a gas containingmolecular hydrogen.

[0034] Catalysts which can advantageously be used in this hydrogenationare those based on a metal selected from the group comprising ruthenium,rhodium, nickel, cobalt and, preferably, iron, it being possible for thecatalysts to contain other elements as promoters. In the case ofiron-based catalysts, suitable promoters are especially one or more,such as two, three, four or five, elements selected from the groupcomprising aluminium, silicon, zirconium, titanium and vanadium.

[0035] Such catalysts and-the process conditions for said reactions canbe found for example in the publications already cited above.

[0036] Suitable amines (III) are cyclic or linear compounds containingat least one carbon-nitrogen double bond or a compound capable offorming at least one carbon-nitrogen double bond, for example by anelimination reaction, or mixtures of such compounds.

[0037] The amine (III) used can advantageously be a compound of theformula

R¹—(CH₂)_(n)—CH═N—(CH₂)_(m)—R²

[0038] in which n and m independently of one another are 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11 or 12, preferably 4, 5 or 6, and

[0039] R¹ and R² independently of one another are —CN or —NH₂,

[0040] or of the formula

[0041] in which R³ is an alkenyl radical having 3, 4, 5, 6, 7, 8, 9, 10or 11 carbon atoms belonging to the ring system.

[0042] In a preferred embodiment, the amine (III) used is selected fromthe group comprising dihydropyrrole, tetrahydropyridine,3-methyltetrahydropyridine, tetrahydroazepine and monounsaturatedcyclododecylamines, or mixtures thereof.

[0043] These amines (III) can be present in the mixture (IV) asindividual compounds or as adducts, for example with a nitrile (I),especially an aminonitrile, said adducts also being referred to asamines (III) in terms of the present invention.

[0044] Such amines (III) and processes for their preparation aregenerally known. Thus tetrahydroazepine can be obtained in mixtures (IV)in the partial catalytic hydrogenation of ADN with a gas containingmolecular hydrogen to give mixtures containing HMD and ACN, normally inamounts of 1 to 10,000 ppm, based on the mixture, by the processesdescribed for the preparation of ACN.

[0045] Also, said amines (III) can be formed by the oxidation of aminessuch as HMD, for example with gases containing molecular oxygen.

[0046] In a preferred embodiment, the mixture (IV) used can be thereaction product obtained from the partial catalytic hydrogenation, suchas gas phase hydrogenation or liquid phase hydrogenation, of dinitriles,especially ADN, with a gas containing molecular hydrogen, in thepresence of a catalyst such as a suspension catalyst or fixed bedcatalyst, said reaction product containing ACN as the aminonitrile (I),HMD as the diamine (II) and tetrahydroazepine as the amine (III) in thecase where ADN is the starting compound, it being possible, if desired,for all or part of any solvent previously used in the hydrogenation tobe separated off. According to previous observations, it can beadvantageous for a catalyst used in the hydrogenation to be separatedoff before the mixture (IV) is used in the process according to theinvention.

[0047] In a preferred embodiment, the mixture (IV) used can be thereaction product obtained from the complete catalytic hydrogenation,such as gas phase hydrogenation or liquid phase hydrogenation, ofdinitriles, especially ADN, with a gas containing molecular hydrogen, inthe presence of a catalyst such as a suspension catalyst or fixed bedcatalyst, said reaction product containing HMD as the diamine (II) andtetrahydroazepine as the amine (III) in the case where ADN is thestarting compound, it being possible, if desired, for all or part of anysolvent previously used in the hydrogenation to be separated off.According to previous observations, it can be advantageous for a.catalyst used in the hydrogenation to be separated off before themixture (IV) is used in the process according to the invention.

[0048] According to the invention, an anionic nucleophile (V) is addedto the mixture (IV).

[0049] The term “anionic” is understood in terms of the presentinvention as meaning that in total the nucleophile (V) carries one ormore, such as two or three, negative charges, preferably one negativecharge.

[0050] The term “nucleophilic” is understood in terms of the presentinvention as meaning the ability of a compound, as described inKoskikallo, Acta Chem. Scand. 23 (1969) pages 1477-1489, to displace theperchlorate group from methyl perchlorate in methanolic solution at 25°C., the remaining methyl group being bonded to the compound (V) via anucleophilic atom of the compound (V).

[0051] A suitable nucleophilic atom of the compound (V) is an atomselected from the group comprising nitrogen, oxygen and sulfur,preferably nitrogen or oxygen.

[0052] According to the invention, the compound (V) is capable of takingup an H⁺ ion to form an acid with a pK_(a) ranging from 7 to 11,preferably from 8 to 10.5, measured in water at 25° C.

[0053] According to the invention, the relative nucleophilicity of thecompound (V), measured in methyl perchlorate/methanol at 25° C.according to Koskikallo, Acta Chem. Scand. 23 (1969) pages 1477-1489,and determined as on pages 1487-1488, ranges from 3.4 to 4.7, preferablyfrom 3.6 to 4.6, when oxygen is the nucleophilic atom, from 4.5 to 5.8,preferably from 4.8 to 5.7, when nitrogen is the nucleophilic atom, andfrom 5.5 to 6.8, preferably from 5.8 to 6.7, when sulfur is thenucleophilic atom.

[0054] When oxygen is the nucleophilic atom of (V), phenates areadvantageously suitable, it being possible for the aromatic ring systemof the phenate to be monosubstituted or polysubstituted, such asdisubstituted or trisubstituted, for example by a C₁- to C₄-alkyl groupsuch as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl ort-butyl, by a halogen such as fluorine, chlorine, bromine or iodine, bya nitro group, by an ester group, by a carbonyl group or by an aminogroup.

[0055] When nitrogen is the nucleophilic atom of (V), suitable compoundsare advantageously those containing the structural unit

[0056] (R⁴ R⁵ N)—

[0057] where R⁴ is the radical of an organic aliphatic, arylaliphatic oraromatic acid, preferably a carboxylic acid or sulfonic acid group, itbeing possible for the radical R⁴ to be substituted as already describedabove for phenate, and

[0058] R⁵ is the radical of an organic aliphatic, arylaliphatic oraromatic acid, preferably a carboxylic acid or sulfonic acid group,hydrogen or a C₁- to C₄-alkyl group such as methyl, ethyl, n-propyl,i-propyl, n-butyl, i-butyl, s-butyl or t-butyl, it being possible forthe radical R⁵ to be substituted as already described above for phenate,

[0059] it being possible for R⁴ and R⁵ to be coupled together other thanby the nitrogen mentioned in the above formula, for example via analkylene, alkylarylene or arylene bridge, preferably via an arylenebridge.

[0060] In a preferred embodiment, the nucleophile (V) used can be alactam anion of the general formula

[0061] in which R⁶ is an alkylene radical having 3, 4, 5, 6, 7, 8, 9, 10or 11 carbon atoms belonging to the ring system, it being possible forthe radical R⁶ to be substituted as already described above for phenate.

[0062] In a preferred embodiment, the nucleophile (V) used can be acaprolactam anion.

[0063] In another particularly preferred embodiment, the nucleophile (V)used can be a benzenesulfonamide anion.

[0064] In another particularly preferred embodiment, the nucleophile (V)used can be a phthalimide anion.

[0065] In another particularly preferred embodiment, the nucleophile (V)used can be phenate.

[0066] For compensation of the negative charge on the anionicnucleophile (V), the latter can be used together with one or morecations preferably selected from the group comprising lithium, sodium,potassium, rubidium, cesium, magnesium and calcium, especiallycomprising lithium, sodium, potassium, magnesium and calcium andparticularly preferably comprising sodium and potassium.

[0067] According to the invention, the nucleophile (V) is added to themixture (IV) in an amount ranging from 0.01 to 10 mol per mole of amine(III) in the mixture (IV).

[0068] Advantageously, the amount of nucleophile (V) can be at least0.05 mol and especially 0.1 mol per mole of amine (III) in the mixture(IV).

[0069] Advantageously, the amount of nucleophile (V) can be at most 1mol, especially at most 0.8 mol and particularly preferably at most 0.5mol per mole of amine (III) in the mixture (IV).

[0070] The nucleophile (V) can be added to the mixture (IV) in a mannerknown per se, for example in conventional mixing apparatuses such astanks, product lines and mixing devices, to give a mixture (VI).

[0071] The nucleophile (V) can be added to the mixture (IV) before themixture (VI) is introduced into a distillation device for separation ofthe nitrile (I) from the mixture (VI). Periods of 5 to 120 minutes,especially of 10 to 60 minutes, have proved advantageous as averagecontact times between the mixture (IV) and the nucleophile (V) beforeintroduction into a distillation device, suitable temperaturesadvantageously ranging from 50 to 170° C.

[0072] Another possibility is to introduce the mixture (IV) and thenucleophile (V) separately into such a device and to carry out thereaction of the mixture (IV) with the nucleophile (V) and the separationof the nitrile (I) from the mixture (VI) in one process step, it beingpossible for the nucleophile (V) to be introduced onto the top, over theentire height onto one of the separation stages or into the bottom ofthe distillation device.

[0073] According to the invention, the nitrile (I) is distilled from themixture (VI) at a temperature ranging from 50 to 170° C., preferablyfrom 70 to 150° C., and a pressure ranging from 0.5 to 100 kPa,preferably from 0.5 to 10 kPa.

[0074] Suitable apparatuses are those conventionally used fordistillation, for example the ones described in Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., vol. 7, John Wiley & Sons,New York, 1979, pages 870-881, such as sieve-plate columns, bubble-capcolumns, packed columns or columns with a side discharge, or variants ofsuch apparatuses in terms of process technology.

[0075] The distillation can be carried out in several columns, such as 2or 3 columns, and advantageously in a single column.

[0076] Aminonitriles and diamines are precursors for the preparation ofindustrially important polyamides such as nylon 6 or nylon 6.6.

EXAMPLES Example 1

[0077] 500 ml of 6-aminocapronitrile with a tetrahydroazepine (THA)content of 300 ppm by weight were treated with 30 mol %, based on THA,of potassium phthalimide and distilled at 96° C. and 0.5 kPa (bottomtemperature 110-115° C.) over a distillation column 1 m in lengthcontaining V2A wire-gauze rings. After 450 ml had distilled over, thedistillation was stopped. 6 ppm of THA were found in the distillate.

Example 2

[0078] 500 ml of 6-aminocapronitrile with a THA content of 1% by weightwere treated with 50 mol %, based on THA, of potassium phthalimide anddistilled at 96° C. and 0.5 kPa (bottom temperature 110-115° C.) over adistillation column 1 m in length containing V2A wire-gauze rings. After450 ml had distilled over, the distillation was stopped. 0.09% by weightof THA was found in the distillate.

Example 3

[0079] For the continuous separation of THA from 6-aminocapronitrile,6-aminocapronitrile with a THA content of 300 ppm by weight was pumpedcontinuously into a 750 ml tank in which a suspension of potassiumphthalimide in 6-aminocapronitrile with a THA content of 300 ppm byweight was being stirred at 65° C. The resulting potassium phthalimidecontent of the solution was 160-170 ppm by weight.

[0080] This solution was pumped continuously out of the tank into a 250ml distillation flask, from which the ACN was distilled at 10 mbar and abottom temperature of 118° C. over a column 30 cm in length containingV2A wire-gauze rings.

[0081] With a loading rate of 210 ml/h, a take-off/reflux ratio of 50:50and a bottom discharge rate of 10 ml/h, 30 ppm by weight of THA werefound in the distillate. The yield of 6-aminocapronitrile was 95%.

We claim:
 1. A process for reducing the content of a monounsaturatedaliphatic amine (III) in a mixture (IV) containing an aminonitrile (I)or a diamine (II), or mixtures thereof, and the amine (III), wherein a)the mixture (IV) is reacted with an anionic nucleophile (V), whichcontains a nucleophilic atom selected from the group comprising oxygen,nitrogen and sulfur, which is capable of taking up an H⁺ ion to form anacid with a pK_(a) ranging from 7 to 11, measured in water at 25° C.,and which has a relative nucleophilicity, measured in methylperchlorate/methanol at 25° C., ranging from 3.4 to 4.7 when oxygen isthe nucleophilic atom, ranging from 4.5 to 5.8 when nitrogen is thenucleophilic atom, and ranging from 5.5 to 6.8 when sulfur is thenucleophilic atom, in an amount ranging from 0.01 to 10 mol per mole ofamine (III) in the mixture (IV), to give a mixture (VI), and b) theaminonitrile (I) or the diamine (II), or mixtures thereof, are distilledfrom the mixture (VI) at a temperature ranging from 50 to 170° C. and apressure ranging from 0.5 to 100 kPa.
 2. A process as claimed in claim 1wherein the aminonitrile (I) used is an aliphatic aminonitrile havingfrom 4 to 12 C atoms.
 3. A process as claimed in claim 1 wherein theaminonitrile (I) used is an aliphatic aminonitrile having from 4 to 12 Catoms selected from the group comprising 4-aminobutyronitrile,5-aminovaleronitrile, 2-methyl-5-aminovaleronitrile, 6-aminocapronitrileand 12-aminododecanenitrile.
 4. A process as claimed in claim 1 whereinthe diamine (II) used is an aliphatic diamine having from 4 to 12 Catoms.
 5. A process as claimed in claim 1 wherein the diamine (II) usedis an aliphatic diamine having from 4 to 12 C atoms selected from thegroup comprising 1,4-diaminobutane, 1,5-diaminopentane,2-methyl-1,5-diaminopentane, 1,6-diaminohexane and 1,12-diaminododecane.6. A process as claimed in any of claims 1 to 5 wherein the amine (III)used is a compound selected from the group comprising dihydropyrrole,tetrahydropyridine, 3-methyltetrahydropyridine, tetrahydroazepine,2-aminoazepan, N-(2-azepano)-1,6-diaminohexane,N-(2-azepano)-6-aminocapronitrile and monounsaturatedcyclododecylamines.
 7. A process as claimed in any of claims 1 to 6wherein the nucleophile (V) used is a benzenesulfonamide anion.
 8. Aprocess as claimed in any of claims 1 to 7 wherein the nucleophile (V)used is a phthalimide anion.
 9. A process as claimed in any of claims 1to 8 wherein the nucleophile (V) used is phenate.
 10. A process asclaimed in any of claims 1 to 9 wherein the nucleophile (V) used is alactam anion of the general formula

in which R⁶ is an alkylene radical having 3, 4, 5, 6, 7, 8, 9, 10 or 11carbon atoms belonging to the ring system.
 11. A process as claimed inany of claims 1 to 10 wherein the nucleophile (V) used is a caprolactamanion.
 12. A process as claimed in any of claims 1 to 11 wherein theanionic nucleophile (V) is used together with a cation selected from thegroup comprising lithium, sodium, potassium, magnesium and calcium.